The present invention relates to an assembly for stabilizing vertebrae, in particular lumbar vertebrae. This assembly can be defined as a relief prosthesis having a dual effect, as will be appreciated below.
It is known that the mobility of two adjacent vertebrae, in particular in the lumbar region, is dependent on the intervertebral disc at the anterior side and pairs of articular surfaces at the posterior side.
The arrangement of the disc and articular surfaces ensures auto-limitation of movements both in the plane perpendicular to the vertebral column, during torsion, and in a sagittal plane, during flexions and extensions of the vertebral column.
The shape, the structure and the height of the disc confer on it additional functions of maintaining lordosis, absorbing shocks and distributing stresses. At the rear, the articular surfaces guide the movements and act as hinges.
The ageing process of the subject leads to disturbances in this anterior/posterior equilibrium involving the discs and the surfaces. Generally, the degeneration of the discs precedes that of the surfaces. Collapse and instability of the discs leads to a partial transfer of the stresses to the posterior columns which are formed by the surfaces, which brings about a loss in the surface congruence and a slackening of the ligaments. This results in deterioration of the articular surfaces, which leads to various pathologies having implications of a mechanical and neurological nature.
In order to treat these pathologies, an anterior arthrodesis has been proposed, by insertion of a graft between the plates of the two vertebrae in question. This graft is usually contained in a rigid cage, known as a “fusion cage”.
However, this technique does not prevent rotational instability which can compromise, in the medium term, the anticipated antalgic result, and it has now been established that the anterior arthrodesis must be complemented by a posterior arthrodesis.
An intervention of this type has limits and disadvantages. It is aimed at severe pathologies which are at an advanced stage and is not without risks, given that the patients are often treated at a relatively late stage in the pathological development. Intervention can further have consequences which are detrimental to adjacent articulations in the medium-term and long-term.
For these reasons, techniques known as “non-fusion” techniques have been developed and relate to the early and palliative treatment of degenerative disc/surface phenomena.
With regard to the disc space, there have been developed various shock-absorbent implants, which are intended to replace the nucleus pulposus, in the form of pairs of pads or elliptical or spiral elements.
These implants are introduced either via an anterior access point, which has the disadvantage of damaging the anterior common vertebral ligament, or via a posterior access point, which has the disadvantage of leading to the sacrifice of a large amount of bone, owing to the space requirement of the implants.
Techniques involving percutaneous injection of a colloid which can be polymerized in situ have also been proposed, as have techniques using solid, disc-like prostheses in the form of two metal plates which enclose a shock-absorbent material and which rest on each of the vertebral plates which are adjacent to the disc.
These techniques are not completely satisfactory as regards the treatment of disc degeneration combined with wear of the surfaces and/or ligament distension.
Devices intended to limit the articular play of the surfaces have also been proposed. A device of this type comprises in particular a continuous woven ligament which is positioned between the spinous processes or along the articular surfaces by means of pedicle screws, and/or a shock-absorbent dividing element which is positioned at the lamina/spinous process junction so as to alleviate the surface play while at the same time stretching the posterior capsule/ligament elements.
It has been found that these techniques are also not completely satisfactory with regard to the above-mentioned treatment.